2 This file is part of GNUnet.
3 (C) 2010 Christian Grothoff (and other contributing authors)
5 GNUnet is free software; you can redistribute it and/or modify
6 it under the terms of the GNU General Public License as published
7 by the Free Software Foundation; either version 2, or (at your
8 option) any later version.
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11 WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 General Public License for more details.
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17 Free Software Foundation, Inc., 59 Temple Place - Suite 330,
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23 * @brief functions related to load calculations
24 * @author Christian Grothoff
27 #include "gnunet_load_lib.h"
29 #define DEBUG_LOAD GNUNET_NO
32 * Values we track for load calculations.
34 struct GNUNET_LOAD_Value
38 * Sum of all datastore delays ever observed (in ms). Note that
39 * delays above 64k ms are excluded (to avoid overflow within
40 * first 4 billion requests).
42 uint64_t cummulative_delay;
45 * Sum of squares of all datastore delays ever observed (in ms). Note that
46 * delays above 64k ms are excluded (to avoid overflow within
47 * first 4 billion requests).
49 uint64_t cummulative_squared_delay;
52 * Total number of requests included in the cummulative datastore delay values.
54 uint64_t cummulative_request_count;
57 * Current running average datastore delay. Its relation to the
58 * average datastore delay and it std. dev. (as calcualted from the
59 * cummulative values) tells us our current load.
64 * How high is the load? 0 for below average, otherwise
65 * the number of std. devs we are above average, or 100 if the
66 * load is so high that we currently cannot calculate it.
74 * Create a new load value.
76 * @return the new load value
78 struct GNUNET_LOAD_Value *
79 GNUNET_LOAD_value_init ()
81 return GNUNET_malloc (sizeof (struct GNUNET_LOAD_Value));
86 * Get the current load.
88 * @param load load handle
89 * @return zero for below-average load, otherwise
90 * number of std. devs we are above average;
91 * 100 if the latest updates were so large
92 * that we could not do proper calculations
95 GNUNET_LOAD_get_load (const struct GNUNET_LOAD_Value *load)
102 * Get the average value given to update so far.
104 * @param load load handle
105 * @return zero if update was never called
108 GNUNET_LOAD_get_average (const struct GNUNET_LOAD_Value *load)
113 if (load->cummulative_request_count == 0)
115 n = ((double) load->cummulative_request_count);
116 sum_val_i = (double) load->cummulative_delay;
117 return sum_val_i / n;
122 * Update the current load.
124 * @param load to update
125 * @param data latest measurement value (for example, delay)
128 GNUNET_LOAD_update (struct GNUNET_LOAD_Value *load,
138 if (data > 64 * 1024)
144 dv = (uint32_t) data;
145 load->cummulative_delay += dv;
146 load->cummulative_squared_delay += dv * dv;
147 load->cummulative_request_count++;
148 load->runavg_delay = ((load->runavg_delay * 7.0) + dv) / 8.0;
149 if (load->cummulative_request_count > 1)
151 /* calcuate std dev of latency; we have for n values of "i" that:
153 avg = (sum val_i) / n
154 stddev = (sum (val_i - avg)^2) / (n-1)
155 = (sum (val_i^2 - 2 avg val_i + avg^2) / (n-1)
156 = (sum (val_i^2) - 2 avg sum (val_i) + n * avg^2) / (n-1)
158 sum_val_i = (double) load->cummulative_delay;
159 n = ((double) load->cummulative_request_count);
161 avgdel = sum_val_i / n;
162 stddev = (((double) load->cummulative_squared_delay) - 2.0 * avgdel * sum_val_i + n * avgdel * avgdel) / nm1;
164 stddev = 0.01; /* must have been rounding error or zero; prevent division by zero */
165 /* now calculate load based on how far out we are from
166 std dev; or if we are below average, simply assume load zero */
167 if (load->runavg_delay < avgdel)
170 load->load = (load->runavg_delay - avgdel) / stddev;